A camera is a video input device mainly including a lens module and an image sensor. Lens modules produced by different vendors are possibly not the same in terms of, for example, a quantity of lenses of a lens module that is produced, composition materials of lenses (such as a plastic nano-composite material and a transparent polymeric material), parameters of a lens module (such as a focal length and an aperture), and whether a special material (such as resin) is added between two lenses. A key factor ensuring quality of photos is to have a lens module with superior performance. If a vendor independently designs a lens module for improving quality of photos, the vendor needs to prevent a competitor from knowing how the lens module is produced and then performing mass production of the lens module. Therefore, to protect a lens module is particularly important.